Conventionally, an internal combustion engine including an intake-side hydraulic drive variable valve timing mechanism is known. See, for example, Patent Document 1. Such an engine changes the valve timing of the intake valves by changing the rotation phase of the intake camshaft relative to the crankshaft with a variable valve timing mechanism.
The engine also includes a lock mechanism for mechanically locking the relative rotation phase of the intake camshaft at an intermediate phase, which is between the most retarded phase and the most advanced phase. Specifically, a vane rotor having vanes is arranged integrally with the intake camshaft. One of the vanes has a lock pin, which is selectively projected and retracted by hydraulic pressure. The vane rotor is accommodated in a housing, which rotates integrally with the crankshaft via the timing chain. The housing has a lock hole, into which the lock pin can be inserted, and a ratchet groove, which extends from the lock hole to the phase retarding side and is shallower than the lock hole.
When a request for locking the relative rotation phase of the intake camshaft at the intermediate phase at stoppage of the engine, the control device for the engine controls the relative rotation phase of the intake camshaft such that the relative rotation phase of the intake camshaft is changed to fall within a predetermined phase range corresponding to the ratchet groove and inserts the lock pin into the ratchet groove. Then, when the intake camshaft is relatively rotated to the intermediate phase through ratchet action, or, in other words, the lock pin is moved to the position of the lock hole through the relative rotation, the lock pin is inserted into the lock hole, thus bringing about a locked state. In this manner, the relative rotation phase of the intake camshaft is mechanically locked at the intermediate phase. The relative rotation phase of the intake camshaft is thus maintained at the intermediate phase, which is suitable for engine start, until the engine is re-started.